1. Field of the Invention
The present invention relates to an electric motor.
2. Description of the Related Art
In an electric motor including a stator provided with slots spaced apart from each other in a circumferential direction and with windings wound around the stator through the slots, and a rotor provided with permanent magnets spaced apart from each other in the circumferential direction and adapted to cooperate with the windings to generate driving torque, it has been known that cogging torque is generated due to various factors. For example, it has been known that during one revolution of an electric motor, cogging torque is generated the same time as the least common multiple of the number of magnetic poles of the rotor and the number of slots of the stator (see the Journal of the Institute of Electrical Engineers of Japan, Vol. 103-B, (1983), pages 711 to 718). In order to prevent such cogging torque, various approaches have been proposed (see JP-A-2005-304150, JP-A-2008-199894, JP-A-2011-55706, JP-A-2005-65479, JP-A-2009-131050 and JP-A-2006-14457).
Therefore, there is a need for an electric motor in which cogging torque is reduced.